This invention relates to an improved sterilizable package wherein color sensitive inks or the like that change color upon sterilization are positioned on the inside of the package and are located so as to prevent the package contents from covering or being contaminated by coming in contact with such inks.
Sterilizable packages or pouches made by marginally heat sealing a clear plastic laminate to surgical grade kraft paper or the like have come into widespread use. The paper portion of such packages is designed to be sufficiently porous to permit gas or steam sterilization but is impervious to bacteria. The plastic laminate is heat sealable to the paper, stable under sterilization conditions, impervious to bacteria and permits visual identification of the package contents. Indicator inks that change color upon sterilization have generally been printed on the exterior, paper side of the package.
Packages such as this are used for medical implements that must be sterile prior to use. The manufacturer or user (such as a hospital or a clinic) is supplied with a package heat sealed around three sides leaving an open end into which the package contents are inserted. The medical implement is then placed in the package and the fourth side is heat sealed to complete the marginal heat seal around the edges of the package. The package and its contents are then subjected to sterilization, either by exposure to ethylene oxide gas or by steam autoclaving. This causes the indicator ink applied to the exterior paper side of the package to change color but this has drawbacks because the indicator ink will change color, being located on the exterior of the package, before the package contents have been exposed to sterilizing gas. This means that sterilization procedures with an extra margin of safety must be followed and the user of the package contents is only assured that the package has undergone sterilization but he has no assurance that the package contents have been exposed to sterilizing gas.
To overcome this it has been proposed to locate the indicator inks closer to the package contents by applying the indicator ink to the inside of the paper member of the sterilizable package (see for example U.S. Pat. No. 3,093,242 to Huyck et al. and U.S. Pat. No. 3,991,881 to Augurt). These efforts, however, have not been entirely satisfactory because the package contents can cover the area imprinted with the indicator ink making it difficult to visually determine the sterile condition of the package and its contents. Moreover, many indicator inks become soft or sticky and some actually run upon exposure to sterilization conditions which means that the package contents can become undesirably contaminated by coming in contact with the indicator inks applied to the interior of the package.